This invention relates to a machine tool and in particular relates to an improved tool holder or spindle in a machine tool.
In general, a spindle of a tool machine has a supporting portion for supporting a tool holder in a tapered opening or other opening. Such a supporting portion is used to be made of a hardened steel and ground for the finishing purpose. A tool holder is attached to the supporting portion of the spindle in such a way that an inserting portion of the tool holder is inserted into the supporting portion of the tool holder. The inserting portion of the tool holder is formed in a shape correspoding to that of the supporting portion of the spindle and made of a hardened steel. The supporting portion and the inserting portion are apt to rust if they are used for a long time and sometimes disfigured. In such a case, machining precision is reduced.
High speed revolution of a spindle causes a bearing to be heated. Such heat is transmitted to the spindle so as to deform the supporting portion. As a result, the fittness of the supporting portion of the spindle to the inserting portion of the tool holder becomes bad in such a way that the tool holder vibrates in machining.